1. Technical Field
The present invention relates to an inertial sensor and a method of manufacturing the same.
2. Description of the Related Art
Recently, an inertial sensor has been used in various fields, for example, the military, such as an artificial satellite, a missile, an unmanned aircraft, or the like, vehicles, such as an air bag, electronic stability control (ESC), a black box for a vehicle, or the like, hand shaking prevention of a camcorder, motion sensing of a mobile phone or a game machine, navigation, or the like.
The inertial sensor generally adopts a configuration in which a mass body is bonded to a flexible substrate such as a membrane, or the like, so as to measure acceleration and angular velocity. Through the configuration, the inertial sensor may calculate the acceleration by measuring inertial force applied to the mass body and may calculate the angular velocity by measuring Coriolis force applied to the mass body.
A process of measuring the acceleration and the angular velocity by using the inertial sensor will be described in detail below. First, the acceleration may be obtained by Newton's law of motion “F=ma”, where “F” represents inertial force applied to the mass body, “m” represents a mass of the mass body, and “a” is acceleration to be measured. Therefore, the acceleration a may be obtained by sensing the force F applied to the mass body and dividing the sensed force F by the mass m of the mass body that is a predetermined value. Further, the angular velocity may be obtained by Coriolis force “F=2mΩ·v”, where “F” represents the Coriolis force applied to the mass body, “m” represents the mass of the mass body, “Ω” represents the angular velocity to be measured, and “v” represents the motion velocity of the mass body. Among others, since the motion velocity v of the mass body and the mass m of the mass body are values that are known in advance, the angular velocity Ω may be obtained by sensing the Coriolis force (F) applied to the mass body.
As described above, when the acceleration a is measured by the inertial sensor, the mass body may be displaced by the inertial force F. In addition, when the angular velocity Ω is measured by the inertial sensor, the mass body is vibrated by the motion velocity v. As described above, in order to measure the acceleration a or the angular velocity Ω, there is a need to move the mass body according to the elasticity of the membrane and in order to improve the sensitivity of the inertial sensor, it is preferable to make the mass of the mass body large and it is preferable to make a spring constant of the membrane small.
FIGS. 1 to 3 are process cross-sectional views showing a method of manufacturing an inertial sensor according to the prior art in a process order. A problem of the prior art will be described with reference to FIGS. 1 to 3.
First, as shown in FIGS. 1 and 2, a mass body 2 and a post 3 are formed by preparing a silicon on insulator (SOI) substrate and then, selectively removing a support substrate 1 of the SOI substrate.
Thereafter, as shown in FIG. 3, an insulating layer 6 (silicon oxide) is selectively removed by supplying an etchant between the mass body 2 and the post 3, thereby forming an adhesive layer 4. In this case, an area of the adhesive layer 4 determines the spring constant of a membrane 5. In detail, as the area of the adhesive layer 4 is narrow, the area of the membrane 5 having elasticity is substantially wide, such that the spring constant is reduced, thereby increasing the sensitivity of the inertial sensor 10. Therefore, although it is preferable that the area of the adhesive layer 4 is gradually narrow, the area of the adhesive layer 4 is affected by a cross sectional area of the mass body 2 even in the case of considering an undercut phenomenon since the adhesive layer 4 is removed by supplying the etchant between the mass body 2 and the post 3. Therefore, in order to narrow the area of the adhesive layer 4, the cross sectional area of the mass body 2 is also narrow. In this case, however, the mass of the mass body 2 is reduced and thus, the sensitivity of the inertial sensor 10 is degraded.
As a result, the inertial sensor 10 according to the prior art has a limitation in improving the sensitivity of the inertial sensor 10 since it is impossible to reduce the spring constant of the membrane 5 while increasing the mass of the mass body 2 in the manufacturing process.